Position or target determining apparatus has previously been proposed, for example, in U.S. Pat. No. 4,225,226, which teaches the use of a scanning laser that interrogates retroreflectors positioned along one side of a field at fixed distances apart. A triangulation technique is used to determine both range and azimuth information. U.S. Pat. No. 4,029,415 teaches the use of a laser scanning a fixed width array of photodetectors, and a triangulation technique is utilized to determine range or distance information. U.S. Pat. No. 4,239,388 teaches use of a laser and an associated reflected laser light detector for identifying a laser light reflecting object by its pattern of reflectivity as a function of time. Furthermore, U.S. Pat. No. 4,307,791 determines position on a factory floor by scanning a pickup mirror over a strip of fluorescent dye. U.S. Pat. No. 4,647,784 teaches another version of triangulation using multiple targets for the control of a vehicle, of which the targets have an embedded identification code.
The first-mentioned patent has the objective of informing a crop dusting airplane pilot of his position over the field to be dusted so that evenly spaced passes may be obtained. It requires complicated electronics including a microprocessor to establish the position for subsequent passes over the field. The second-mentioned patent has for its object the surveying of land but requires an operator to move the rod on which the fixed width array of photodetectors is mounted. The third-mentioned patent has for its object the determination of objects on the ground by an aircraft or the like flying overhead and directing a laser beam downward to be reflected from the ground or the object. The fourth-mentioned patent relies on multiple signal components from the fluorescent strip on the floor for analysis of position, and the fifth-mentioned patent uses multiple bar coded targets without a means for handling distance effects on bar code timing.